With the wide application of computers and the rapid development of information and related industries, the currently available central processing unit or chip for computers has a surprisingly high operation speed. However, the extremely high-speed central processing unit or chip also produces very large amount of heat during its operation. The produced heat would seriously adversely affect the stable performance of the central processing unit or the chip, if it were not properly and timely radiated or dissipated. A common practice for the information and other related industries to solve this problem is to mount a radiator on a top of the central processing unit or the chip and a cooling fan on the radiator to enable quick dissipation of heat produced by the central processing unit or the chip.
Most of the current radiators are made of an aluminum alloy material that has low material cost and provides relatively good thermal conducting effect when compared with other materials. Therefore, other available materials are used to make the radiators only in a few special cases. Under this condition, the best way to carry away the heat transferred to the radiator is to increase as much as possible the contact area between the radiator and the surrounding air. A radiator having a large volume could only slow the rising of temperature thereof when it has only a small contact area with the surrounding air.
FIGS. 1 to 4 shows a conventional cooling fan 11 for mounting on a plurality of parallel radiation fins 121 of a radiator 12. As shown, the cooling fan 11 mainly includes a seat 112 having mounting holes 112a provided at predetermined positions thereon, and an air-guiding fan 113 pivotally connected to the seat 112. The seat 112 includes a centered driving section 112b and a plurality of supporting sections 112c extended between the centered driving section 112b and the seat 112. The air-guiding fan 113 includes a hub 113a and a plurality of blades 113b generally radially spaced around an outer periphery of the hub 113a. 
The cooling fan 11 is connected to the top of the radiation fins 121 of the radiator 12 by screwing fastening elements 111, such as screws, into the mounting holes 112a on the seat 112. The radiator 12 is then caused to closely bear against a chip 131 mounted on a circuit board 13, and finally assembled to the circuit board 13.
When the driving section 112b drives the air-guiding fan 113 to rotate, air in the space above and surrounding the cooling fan 11 is brought to move into an air inlet 112d of the seat 112 and out of an air outlet 112e of the seat 112. Since the supporting sections 112c are normally radially extended from the driving section 112b to locate between the driving section 112b and the air outlet 112e of the seat 112 and cross with the parallelly arranged radiation fins 121 of the radiator 12, they prevent the air flown out of the seat 112 from smoothly flowing toward the radiator 12, resulting in reduced airflow that could reach at the radiator 12 and reduced contact area of the radiator 12 with surrounding air. Since the produced heat is carried away by air, the reduced airflow produced by the cooling fan 11 would decrease the contact area between the radiator and the air to result in poor radiating effect. Even a high-power or a high-speed cooling fan would not be able to satisfactorily radiate heat produced by the chip 131 on the circuit board 13 when the cooling fan 11 does not effectively increase the contact area between the radiator and surrounding air. In this case, the high-power or high-speed cooling fan would only produce the problems of large noises and high manufacturing cost.
It is therefore tried by the inventor to develop a cooling fan that eliminates the drawbacks existed in the conventional cooling fans.